More than just hormones: H295R cells as predictors of reproductive toxicity

Evaluating H295R steroidogenesis assay data for robust interpretation

The in vitro H295R steroidogenesis assay (OECD TG 456) is used to determine a chemical's potential to interfere with steroid hormone synthesis/metabolism. As positive outcomes in this assay can trigger significant higher tiered testing, we compiled a stakeholder database of reference and test item H295R data to characterize assay outcomes. Information concerning whether a Level 5 reproductive toxicity study was triggered due to a positive outcome in the H295R assay was also included. Quality control acceptance criteria were not always achieved, suggesting this assay is challenging to conduct within the guideline specifications. Analysis of test item data demonstrated that pairwise significance testing to controls allowed for overly sensitive statistically significant positive outcomes, which likely contribute to the assay's high positive hit rate. Complementary interpretation criteria (e.g., 1.5-fold change threshold) markedly reduced the rate of equivocal and positive outcomes thus improving identification of robust positive effects in the assay. Finally, a case study (positive H295R outcome and no endocrine adversity in vivo) is presented, which suggests that stricter data interpretation criteria could refine necessary in vivo follow-up testing. Overall, the described additional criteria could improve H295R data interpretation and help inform on how to best leverage this assay for regulatory purposes.

Studying paraben-induced estrogen receptor- and steroid hormone-related endocrine disruption effects via multi-level approaches

Increasing concerns have been raised on the health risks of parabens in the regard of their widespread applications and potential endocrine disrupting activities. In this study, four typical parabens, including methyl paraben (MeP), ethyl paraben (EtP), propyl paraben (PrP), and butyl paraben (BuP) were systematically investigated for their estrogen receptor- and steroid hormone-related endocrine disruptions using multi-level approaches. Paraben exposure promoted the proliferation of MCF-7 cells, increased the luciferase activity in MVLN cells, and induced the vitellogenin (vtg) expression in zebrafish larvae, showing the typical estrogenic effects. The in vitro protein assays further revealed that PrP and BuP could bind with two isoforms of estrogen receptors (ERs). The estrogenic activities of parabens were predicted to be positively correlated with their chemical structure complexity by using molecular docking analysis. Furthermore, the synthesis and secretion of estradiol (E2) and testosterone (T) were significantly disturbed in H295R cells and zebrafish larvae, which could be regulated by paraben-induced transcriptional disturbance in both in vitro steroidogenesis and in vivo hypothalamic-pituitary-gonadal (HPG) axis. Parabens could disturb the endocrine system by activating the ERs and disrupting the steroid hormone synthesis and secretion, suggesting their potential deleterious risks to the environment and human health.

Extended steroid profiling in H295R cells provides deeper insight into chemical-induced disturbances of steroidogenesis: Exemplified by prochloraz and anabolic steroids

Human adrenocortical H295R cells have been validated by the OECD Test Guideline 456 to detect chemicals disrupting testosterone and 17β-estradiol (estradiol) biosynthesis. This study evaluated a novel approach to detect disturbances of steroidogenesis in H295R cells, exemplified by prochloraz and five anabolic steroids. Steroid profiles were assessed by an untargeted LC-MS-based method, providing a relative quantification of 57 steroids annotated according to their accurate masses and retention times. Such a panel of steroids included several mineralocorticoids, glucocorticoids, progestins and adrenal androgens. The coverage of a high number of metabolites in this extended steroid profiling facilitated grouping of chemicals with similar effects and detecting subtler differences between chemicals. It allowed, for example, distinguishing between the effects of turinabol and oxymetholone, supposed to act similarly in a previous characterization including only nine adrenal steroids. Furthermore, the results revealed that product/substrate ratios can provide superior information on altered enzyme activities compared to individual metabolite levels. For example, the 17α-hydroxypregnenolone/pregnenolone ratio was found to be a more sensitive marker for detecting 17α-hydroxylase inhibition by prochloraz than the corresponding individual steroids. These results illustrate that chemical grouping and calculation of product/substrate ratios can provide valuable information on mode-of-action and help prioritizing further experimental work.

Evaluating structure-based activity in a high-throughput assay for steroid biosynthesis

Data from a high-throughput human adrenocortical carcinoma assay (HT-H295R) for steroid hormone biosynthesis are available for >2000 chemicals in single concentration and 654 chemicals in multi-concentration (mc). Previously, a metric describing the effect size of a chemical on the biosynthesis of 11 hormones was derived using mc data referred to as the maximum mean Mahalanobis distance (maxmMd). However, mc HT-H295R assay data remain unavailable for many chemicals. This work leverages existing HT-H295R assay data by constructing structure-activity relationships to make predictions for data-poor chemicals, including: (1) identification of individual structural descriptors, known as ToxPrint chemotypes, associated with increased odds of affecting estrogen or androgen synthesis; (2) a random forest (RF) classifier using physicochemical property descriptors to predict HT-H295R maxmMd binary (positive or negative) outcomes; and, (3) a local approach to predict maxmMd binary outcomes using nearest neighbors (NNs) based on two types of chemical fingerprints (chemotype or Morgan). Individual chemotypes demonstrated high specificity (85-98%) for modulators of estrogen and androgen synthesis but with low sensitivity. The best RF model for maxmMd classification included 13 predicted physicochemical descriptors, yielding a balanced accuracy (BA) of 71% with only modest improvement when hundreds of structural features were added. The best two NN models for binary maxmMd prediction demonstrated BAs of 85 and 81% using chemotype and Morgan fingerprints, respectively. Using an external test set of 6302 chemicals (lacking HT-H295R data), 1241 were identified as putative estrogen and androgen modulators. Combined results across the three classification models (global RF model and two local NN models) predict that 1033 of the 6302 chemicals would be more likely to affect HT-H295R bioactivity. Together, these in silico approaches can efficiently prioritize thousands of untested chemicals for screening to further evaluate their effects on steroid biosynthesis.

Exposure to difenoconazole induces reproductive toxicity in zebrafish by interfering with gamete maturation and reproductive behavior

Difenoconazole (DCZ) is a triazole fungicide that negatively affects aquatic organisms and humans. However, data regarding the reproductive toxicity of DCZ are insufficient. In this study, we used zebrafish (from 2 h post-fertilization [hpf] to adulthood) as a model to evaluate whether DCZ at environmentally relevant concentrations (0.1, 1.0, and 10.0 μg/L) induces reproductive toxicity. After exposure to DCZ, egg production and fertilization rates were reduced by 1.0 and 10.0 μg/L. A significant decrease in gamete frequency (late vitellogenic oocytes and spermatozoa) was observed at 10.0 μg/L. The concentrations of 17β-estradiol (E2), testosterone (T), and vitellogenin (VTG) were disrupted in females and males by 1.0 and 10.0 μg/L. Exposure to 10.0 μg/L DCZ significantly inhibited the contact time between female and male fish, which was mainly achieved by affecting male fish. The transcription of genes involved in the hypothalamus-pituitary-gonad (HPG) axis was significantly changed after treatment with DCZ. Overall, these data show that the endocrine-disrupting effect of DCZ on the zebrafish HPG axis inhibited gamete maturation and disrupted reproductive behavior, reducing fertility.

A discovery-based undergraduate laboratory exercise to investigate the effect of potential endocrine disruptors on sex hormones using human cell culture

In this laboratory exercise, students have an opportunity to evaluate the potential endocrine disrupting abilities of environmental chemicals of their choice using human cell culture. Over the course of 9 weeks, students learn how to aseptically handle and manipulate cells, perform and analyze a cytotoxicity assay and an enzyme-linked immunosorbent assay. Following completion of the module, the majority of students reported large or very large gains not only in laboratory performance, but also in understanding of the scientific literature and research process, as well as scientific communication skills. The student survey results imply that this authentic laboratory experience improves students' scientific literacy and prepares them for future careers in science.

Human adrenocortical carcinoma cell line (NCI-H295R): An in vitro screening model for the assessment of endocrine disruptors' actions on steroidogenesis with an emphasis on cell ultrastructural features

Cell lines as an in vitro model for xenobiotic screening and toxicity studies provide a very important tool in the field of scientific research at the level of molecular pathways and gene expression. Good cell culture practice and intracellular characterization, as well as physiological properties of the cell line are of critical importance for in vitro reproductive toxicity testing of various endocrine-disrupting chemicals. The NCI-H295R, human adrenocarcinoma cell line, is the most widely used in vitro cellular system to study the human adrenal steroidogenic pathway at the level of hormone production and gene expression, as it expresses genes that encode for all the key enzymes for steroidogenesis. In this review, we aim to highlight the information considering the origin, development, physiological and ultrastructural characteristics of the NCI-H295R cell line. The review also creates a broad overview of the cell line usage in various range of studies related to the steroidogenesis issues. To our best knowledge, the paper provides the first report of quantitative data (ex novo) from stereological estimates of component (volume, surface) densities of nuclei, mitochondria, and lipid droplets of the NCI-H295R cells. Such ultrastructural measurements can be valuable in the assessment of underlying mechanisms of changes in the cell steroid hormone production induced by the action of diverse endocrine disruptors. Thus, they can significantly contribute to complexity of structure-function relationships in association with steroidogenesis.

Forskolin Induces Endocrine Disturbance in Human JEG-3 Placental Cells

Forskolin, used in folk medicine since ancient times, is now available as a dietary supplement, with an indication as a fat burner and appetite suppressant. However, the safety of forskolin is poorly documented especially for pregnant women. The question that we raised is what about the safety of forskolin in pregnant women? As the placenta, an endocrine organ, is the key organ of pregnancy, we evaluated the in vitro placental toxicity of forskolin. We focused first on the activation of a P2X7 degenerative receptor as a key biomarker for placental toxicity, and second on steroid and peptide hormonal secretion. We observed that forskolin activated P2X7 receptors and disturbed estradiol, progesterone, hPL and hyperglycosylated hCG secretion in human placental JEG-Tox cells. To the best of our knowledge, we highlighted, for the first time, that forskolin induced endocrine disturbance in placental cells. Forskolin does not appear to be a safe product for pregnant women and restrictions should be taken.

In vitro and in silico approach to study the hormonal activities of the alternative plasticizer tri-(2-ethylhexyl) trimellitate TEHTM and its metabolites

Tri-(2-ethylhexyl) trimellitate (TEHTM) is a plasticizer for polyvinyl chloride (PVC) material used in medical devices. It is an alternative to di-(2-ethylhexyl) phthalate (DEHP), a well-known reprotoxic and endocrine disruptor. As plasticizers are known to easily migrate when in contact with fatty biological fluids, patient exposure to TEHTM is highly probable. However, there is currently no data on the potential endocrine-disrupting effects of its human metabolites. To evaluate the effects of TEHTM metabolites on endocrine activity, they were first synthesized and their effects on estrogen, androgen and thyroid receptors, as well as steroid synthesis, were investigated by combining in vitro and in silico approaches. Among the primary metabolites, only 4-MEHTM (4-mono-(2-ethylhexyl) trimellitate) showed agonist activities on ERs and TRs, while three diesters were TR antagonists at non-cytotoxic concentrations. These results were completed by docking experiments which specified the ER and TR isoforms involved. A mixture of 2/1-MEHTM significantly increased the estradiol level and reduced the testosterone level in H295R cell culture supernatants. The oxidized secondary metabolites of TEHTM had no effect on ER, AR, TR receptors or on steroid hormone synthesis. Among the fourteen metabolites, these data showed that two of them (4-MEHTM and 2/1-MEHTM) induced effect on hormonal activities in vitro. However, by comparing the concentrations of the primary metabolites found in human urine with the active concentrations determined in bioassays, it can be suggested that the metabolites will not be active with regard to estrogen, androgen, thyroid receptors and steroidogenesis-mediated effects.

Effects of fast food packaging plasticizers and their metabolites on steroid hormone synthesis in H295R cells

The health risks of exposure to plasticizers have received widespread attention, however, little is known about the effects of fast food packaging plasticizers on steroid hormone synthesis. In the present study, the types and migration of plasticizers in some commonly used fast-food packaging materials were detected by GC-MS, and the interference effects of these plasticizers and their metabolites on steroid hormone synthesis in the human body were evaluated by the H295R steroidogenesis assay. The GC-MS results showed that the main plasticizer compounds that migrated from fast food packaging into food were di(2-ethylhexyl) phthalate (DEHP), dibutyl phthalate (DBP) and bis(2-ethylhexyl) adipate (DEHA). Exposure to these chemicals (100-1000 μM) can significantly reduce the viability of H295R cells in a dose-response manner, and these plasticizers and their metabolites that migrated into oily foods at high temperatures (0.25-25 μM) could significantly increase the E2 level and reduce the T level in H295R cells. According to the qRT-PCR data, 0.25 to 25 μM mono(2-ethylhexyl) phthalate (MEHP) significantly upregulated the expression levels of 17β-HSD1 and CYP19A1, and downregulated those of CYP17A1, CYP11A1 and StAR. The Western blot results were consistent with those of qRT-PCR. In summary, these results indicated that even exposure to low concentrations (≤1 mg/l or 2.5 μM) of these chemicals and their metabolites can cause significant endocrine-disrupting effects.

Ginsenoside Rd attenuates ACTH-induced corticosterone secretion by blocking the MC2R-cAMP/PKA/CREB pathway in Y1 mouse adrenocortical cells

BACKGROUND

Higher levels of glucocorticoids (GCs), and impaired regulation of the hypothalamic-pituitary-adrenal (HPA) axis may cause or exacerbate the occurrence of metabolic and psychiatric disorders. It has been reported that ginseng saponin extract (GSE) has an inhibitory effect on the hyperactivity of the HPA axis induced by stresses and increased corticosterone level induced by intraperitoneal injection of adrenocorticotrophic hormone (ACTH) in mice. However, the molecular mechanisms by which GSE and its active ginsenosides inhibit corticosterone secretion remain elusive.

MAIN METHODS

Y1 mouse adrenocortical cells were treated with ACTH for up to 60 min to establish a cell model of corticosterone secretion. After treatment with different concentrations of GSE or ginsenoside monomers for 24 h prior to the addition of ACTH, analyses of cAMP content, PKA activity, and the levels of steroidogenesis regulators, melanocortin-2 receptor (MC2R), and melanocortin-2 receptor accessory protein (MRAP) in ACTH-induced Y1 cells were performed.

RESULTS

We demonstrated that GSE inhibits ACTH-stimulated corticosterone production in Y1 cells by inhibiting factors critical for steroid synthesis. Ginsenoside Rd, an active ingredient of GSE, inhibits corticosterone secretion in the cells and impedes ACTH-induced corticosterone biosynthesis through down-regulation of proteins in the cAMP/PKA/CREB signaling pathway. In addition, Western blot and qPCR analyses showed that ginsenoside Rd attenuated the induction of MC2R and MRAP by ACTH.

CONCLUSION

Our findings indicate that ginsenoside Rd inhibits ACTH-induced corticosterone production through blockading the MC2R-cAMP/PKA/CREB pathway in adrenocortical cells. Overall, this mechanism may represent an important therapeutic option for the treatment of stress-related disorders, further supporting the pharmacological benefits of ginseng.

Determination of Endocrine Disruption Potential of Bisphenol A Alternatives in Food Contact Materials Using In Vitro Assays: State of the Art and Future Challenges

Alternatives to bisphenol A (BPA) are developed for food contact materials as a result of increasing evidence of exposure-correlated harmful effects of BPA. In vitro assays provide the fast, affordable, and mechanism insightful ways to screen endocrine disruption (ED), which is a major concern of new BPA alternatives. In this review, we summarize the safety and regulation information on the alternatives to BPA, review the state of the art of in vitro assays for ED evaluation, highlight their advantages and limitations, and discuss the challenges and future research needs. Our review shows that ligand binding, reporter gene, cell proliferation, and steroidogenesis are four commonly used in vitro assays to determine the ED at the response of receptor, gene transcription, and whole cell level. Major challenges are found from in vitro-in vivo translation and identification of ED chemicals in polymers. More studies on these areas are needed in the future.

Effects of defined mixtures of POPs and endocrine disruptors on the steroid metabolome of the human H295R adrenocortical cell line

The presence of environmental pollutants in our ecosystem may impose harmful health effects to wildlife and humans. Several of these toxic chemicals have a potential to interfere with the endocrine system. The adrenal cortex has been identified as the main target organ affected by endocrine disrupting chemicals. The aim of this work was to assess exposure effects of defined and environmentally relevant mixtures of chlorinated, brominated and perfluorinated chemicals on steroidogenesis, using the H295R adrenocortical cell line model in combination with a newly developed liquid chromatography tandem mass spectrometry (LC-MS/MS) method. By using this approach, we could simultaneously analyze 19 of the steroids in the steroid biosynthesis pathway, revealing a deeper insight into possible disruption of steroidogenesis. Our results showed a noticeable down-regulation in steroid production when cells were exposed to the highest concentration of a mixture of brominated and fluorinated compounds (10,000-times human blood values). In contrast, up-regulation was observed with estrone under the same experimental condition, as well as with some other steroids when cells were exposed to a perfluorinated mixture (1000-times human blood values), and the mixture of chlorinated and fluorinated compounds. Interestingly, the low concentration of the perfluorinated mixture alone produced a significant, albeit small, down-regulation of pregnenolone, and the total mixture a similar effect on 17-hydroxypregnenolone. Other mixtures resulted in only slight deviations from the control. Indication of synergistic effects were noted when we used a statistical model to improve data interpretation. A potential for adverse outcomes of human exposures is indicated, pointing to the need for further investigation into these mixtures.

High-Throughput H295R Steroidogenesis Assay: Utility as an Alternative and a Statistical Approach to Characterize Effects on Steroidogenesis

The U.S. Environmental Protection Agency Endocrine Disruptor Screening Program and the Organization for Economic Co-operation and Development (OECD) have used the human adrenocarcinoma (H295R) cell-based assay to predict chemical perturbation of androgen and estrogen production. Recently, a high-throughput H295R (HT-H295R) assay was developed as part of the ToxCast program that includes measurement of 11 hormones, including progestagens, corticosteroids, androgens, and estrogens. To date, 2012 chemicals have been screened at 1 concentration; of these, 656 chemicals have been screened in concentration-response. The objectives of this work were to: (1) develop an integrated analysis of chemical-mediated effects on steroidogenesis in the HT-H295R assay and (2) evaluate whether the HT-H295R assay predicts estrogen and androgen production specifically via comparison with the OECD-validated H295R assay. To support application of HT-H295R assay data to weight-of-evidence and prioritization tasks, a single numeric value based on Mahalanobis distances was computed for 654 chemicals to indicate the magnitude of effects on the synthesis of 11 hormones. The maximum mean Mahalanobis distance (maxmMd) values were high for strong modulators (prochloraz, mifepristone) and lower for moderate modulators (atrazine, molinate). Twenty-five of 28 reference chemicals used for OECD validation were screened in the HT-H295R assay, and produced qualitatively similar results, with accuracies of 0.90/0.75 and 0.81/0.91 for increased/decreased testosterone and estradiol production, respectively. The HT-H295R assay provides robust information regarding estrogen and androgen production, as well as additional hormones. The maxmMd from this integrated analysis may provide a data-driven approach to prioritizing lists of chemicals for putative effects on steroidogenesis.

Nutlin-3a as a novel anticancer agent for adrenocortical carcinoma with CTNNB1 mutation

Adrenocortical carcinoma (ACC) is a rare malignancy, and CTNNB1 is frequently mutated in ACC. Our study aims to screen for effective agents with antineoplastic activity against ACC with CTNNB1 mutation. In‐silico screening of the Genomics of Drug Sensitivity in Cancer (GDSC) database was conducted. Drug sensitivity in cells with CTNNB1 mutation was analyzed and further in vitro and in vivo studies were performed using the compound. Only one compound, Nutlin‐3a, an MDM2 inhibitor, was significantly sensitive in 18 cancer cells with CTNNB1 mutation. Further analysis of the 18 cells revealed no significant efficacy between cells with both CTNNB1 and TP53 mutations indicating concomitant TP53 mutation did not impact on drug efficacy. We verified that Nutlin‐3a inhibited cellular proliferation in ACC cell line NCI‐H295R which harbored CTNNB1 mutation but not in SW13 cells which did not. Nutlin‐3a induced cell apoptosis and G1 cell‐cycle arrest in NCI‐H295R cells. Nutlin‐3a also decreased cellular migration and inhibited epithelial‐to‐mesenchymal transition (EMT) process in terms of EMT index. Nutlin‐3a resulted in decreased β‐catenin level independent of p53 level in NCI‐H295R but not SW13 cells. We also evaluated the effect of Nutlin‐3a on hormonal secretion of NCI‐H295R cells and found it resulted in decreased levels of cortisol, androgen, and progesterone. Nutlin‐3a treatment inhibited ACC tumor growth with no observed toxicity in mice in vivo. Our study has revealed that Nutlin‐3a potently inhibits ACC with CTNNB1 mutation. How p53/MDM2 axis coordinates with Wnt/beta‐Catenin signaling in ACC warrants further study.

Synthetic Phenolic Antioxidants Cause Perturbation in Steroidogenesis in Vitro and in Vivo

Synthetic phenolic antioxidants (SPAs) are closely correlated with human life due to their extensive usages, and increasing concerns have been raised on their biosafety. The previous controversial findings caused continuous debates on their potential endocrine disrupting effects. In the present study, four commonly used SPAs, including butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), tert-butyl hydroquinone (TBHQ) and 2,2'-methylenebis(6-tert-butyl-4-methylphenol) (AO2246), were investigated for their estrogenic effects, and the results from in vitro screening assays showed SPAs themselves had negligible estrogen receptor binding affinities. Nevertheless, significant increase in E₂ secretion was observed in H295R cells treated with SPAs, especially for BHA. The transcriptional levels of steroidogenic enzymes, including StAR, 3βHSD, CYP11B1, and CYP11B2 were up-regulated via the mediation of protein kinase A (PKA) signaling pathway. In vivo experiment confirmed that waterborne exposure to BHA disturbed E₂ and testosterone (T) levels in zebrafish gonad, thus causing potential estrogenic effects through the regulation of hypothalamic-pituitary-gonadal-liver axis (HPGL-axis). Accordingly, this study has provided new insights for SPA-induced endocrine disrupting effects. Considering the allowable maximum level of individual BHA or in combination with TBHQ and BHT in foodstuffs (200 mg kg^-1), the perturbation in steroidogenesis observed for relatively low concentrations of SPAs would need more public attention.

2015 Lush Science Prize

The Lush Prize supports animal-free testing by rewarding the most effective projects and individuals who have been working toward the goal of replacing animals in product or ingredient safety testing. Prizes are awarded for developments in five strategic areas: Science; Lobbying; Training; Public Awareness; and Young Researchers. Should there be a major breakthrough in 21st century toxicology, a Black Box Prize equivalent to the entire annual fund of £250,000 is awarded. A Background Paper is prepared each year, prior to the judging process, to provide the panel with a brief overview of current developments in the field of Replacement alternatives, particularly those relevant to the concept of toxicity pathways. The Background Paper includes information on recent work by the relevant scientific institutions and projects in this area, including AXLR8, the OECD, The Hamner Institutes, the Human Toxome Project, EURL ECVAM, ICCVAM, the US Tox21 Programme, the ToxCast programme, and the Human Toxicology Project Consortium. Recent developments in toxicity pathway research are also assessed by reviewing the relevant literature (including conference proceedings), and the abstracts and papers receiving the highest score are presented to the judges for consideration.

Disruption of steroidogenesis: Cell models for mechanistic investigations and as screening tools

In the modern world, humans are exposed during their whole life to a large number of synthetic chemicals. Some of these chemicals have the potential to disrupt endocrine functions and contribute to the development and/or progression of major diseases. Every year approximately 1000 novel chemicals, used in industrial production, agriculture, consumer products or as pharmaceuticals, are reaching the market, often with limited safety assessment regarding potential endocrine activities. Steroids are essential endocrine hormones, and the importance of the steroidogenesis pathway as a target for endocrine disrupting chemicals (EDCs) has been recognized by leading scientists and authorities. Cell lines have a prominent role in the initial stages of toxicity assessment, i.e. for mechanistic investigations and for the medium to high throughput analysis of chemicals for potential steroidogenesis disrupting activities. Nevertheless, the users have to be aware of the limitations of the existing cell models in order to apply them properly, and there is a great demand for improved cell-based testing systems and protocols. This review intends to provide an overview of the available cell lines for studying effects of chemicals on gonadal and adrenal steroidogenesis, their use and limitations, as well as the need for future improvements of cell-based testing systems and protocols.

Stimulus-selective induction of the orphan nuclear receptor NGFIB underlies different influences of angiotensin II and potassium on the human adrenal gland zona glomerulosa-specific 3β-HSD isoform gene expression in adrenocortical H295R cells

In the adrenal, the type I 3β-hydroxysteroid dehydrogenase (HSD3B1) is expressed exclusively in the zona glomerulosa (ZG), where aldosterone is produced. Angiotensin II (AngII) and potassium (K(+)) are the major physiological regulators of aldosterone synthesis. However, their respective roles in regulation of aldosterone synthesis are not fully defined, particularly in terms of transcriptional regulation of steroidogenic enzyme genes. We previously showed that AngII can stimulate expression of HSD3B1. But, K(+) responsiveness of this gene has remained unexplored. Here, we report that K(+) stimulation lacks the ability to induce HSD3B1 expression in human adrenocortical H295R cells. Both AngII and K(+) were able to enhance transcription of the aldosterone synthase gene (CYP11B2). Promoter analysis revealed that although both AngII and K(+) activate transcription from the Ca(2+)/cAMP-responsive element (CRE) located in the CYP11B2 promoter, the orphan nuclear receptor NGFIB-responsive element (NBRE) located in the HSD3B1 promoter fails to respond to K(+), being only able to enhance transcription after AngII treatment. We found that induction of de novo protein synthesis of NGFIB occurs only after AngII treatment. This sharply contrasts with the phosphorylation that occurs in response to both AngII and K(+) on the CREB/ATF family transcription factor ATF2. Chromatin immunoprecipitation assay confirmed that the NGFIB protein occupies the HSD3B1 promoter only after AngII, while ATF2 binds to the CYP11B2 promoter in response to both AngII and K(+). These data provide evidence that downstream signals from AngII and K(+) can be uncoupled in the regulation of HSD3B1 in the human adrenocortical H295R cells.